Vehicles may include a transmission coupled to an engine in order to provide more flexible use of the power output of the engine. The transmission may provide a number of gear ratios that enable the vehicle to travel at relatively wide range of speeds or conditions that might be impractical without a transmission. Some transmissions are configured to change gear ratios automatically in order to improve the ease of operation of the vehicle as it is operated through its speed range.
The circumstances under which the transmission shifts gears may affect the efficiency of operation of the vehicle. For example, the time at which the transmission shifts gears and the gears selected by the transmission may result in operating the engine at more efficient engine speeds and power outputs. For example, in general, it is more efficient to operate an engine at relatively lower engine speeds for a given power output. However, under certain conditions, it may be preferable to operate an engine in a range of engine speeds that result in relatively higher engine performance at the expense of efficiency. For example, if the vehicle is heavily loaded and/or travelling up a relatively steep or long grade, it may be preferable for the transmission to select gear ratios that provide improved performance even if efficiency may suffer. As a result, it may be desirable to operate the transmission under certain conditions so that the efficiency of the vehicle is improved, while under other conditions, so that the performance of the vehicle is improved.
A method for selecting a shift schedule for a transmission in a motor vehicle is disclosed in U.S. Pat. No. 7,499,784 B2 to Kresse (“the '784 patent”). In particular, the method disclosed in the '784 patent includes the steps of determining whether a signal-to-noise ratio exceeds a threshold and calculating a tractive effort of the motor vehicle. The method thereafter includes estimating vehicle mass and road grade from the tractive effort using a recursive least squares estimator with multiple forgetting when the signal-to-noise ratio exceeds the threshold. When the signal-to-noise ratio does not exceed the threshold, vehicle mass is selected, and the road grade is estimated from the vehicle mass and tractive effort. Thereafter, the method includes selecting a shift schedule based on the vehicle mass and the estimated road grade.
Although the method disclosed in the '784 patent includes selecting a shift schedule based on estimations of the vehicle mass and road grade, the manner in which the estimations are carried out may suffer from a number of possible drawbacks. For example, the estimations may lack accuracy due, for example, to reliance on assumptions that are inaccurate. Therefore, it may be desirable to provide a system and method for controlling a transmission that selects shift schedules for the transmission in a more desirable manner.